Mogroside V, also known as momordica-glycosides, is the main sweet component of Siraitia grosvenori of Genus Siraitia in Cucurbitaceae. Its sweetness is 350 times of sucrose. At present, seven monomer components have been identified, among which, mogroside V and Siamenoside I have the highest sweetness. Mogroside has the characteristics of low sugar, low calorie and the like, has the improvement effects to the immune system, liver and blood glucose of the modern consumers, and can meet the health requirements of contemporary consumers. Compared with the traditional natural sweetener stevioside, mogroside V has a mouthfeel closer to sucrose, no bitter taste, which can make up for the deficiencies of stevioside to some extent.
With the continuous increasing of the quantity demanded and quality requirement of mogroside V in the market, especially the more stringent requirements for improvement of mouthfeel and reduction of pesticide residues, the task of improving the mouthfeel and quality of mogroside V is extremely urgent. However, the compositions of the Siraitia grosvenori extract are complex, which increase the difficulty of separating and purifying mogroside V in the preparation process. In addition, the low content of mogroside V in natural Siraitia grosvenori results in high production cost of mogroside V, which cannot meet the demand of mass marketization of mogroside V.
In the prior art, mogroside V is separated and purified mainly by the following processes: adsorbing and enriching mogroside V by ion exchange resin and macroporous adsorption resin, adding deionized water or purified water to wash the column so as to remove residual impurities and partial pigments; and then adding organic solvent such as ethanol so as to desorb the mogroside V from the macroporous adsorption resin, thereby obtaining mogroside V. For example, Reference Document 1 (Chinese Patent Application Publication No. CN101177444A) discloses “a method for extracting mogroside from Siraitia grosvenori”, wherein the steps of extraction, ultrafiltration, concentration, enrichment of mogroside by macroporous adsorption resin, washing with purified water, elution with ethanol, and recovery of ethanol are performed in order to give a Siraitia grosvenori extract containing mogroside. The products obtained by ethanol desorption have low content of mogroside and comprise many bitter impurities, which greatly affect the mouthfeel, and the ability to remove residual pesticides of this method cannot meet the increasingly stringent quality requirements. The tedious elution step and the recovery of ethanol also increase the time and cost of the whole production process.
In order to make up for the deficiency of macroporous resin adsorption-ethanol elution technology, it is needed to refine and purify Siraitia grosvenori extract by using a variety of resins or materials having different properties in the prior art. For example, Reference Document 2 (Chinese Patent Publication No. CN101690573B) discloses “a method for producing a Siraitia grosvenori extract with a content of mogroside V of 60% or more”, in which the Siraitia grosvenori is subjected to crush, saccharification, extraction, concentration, centrifugation, refinement with ion exchange resin, enrichment with macroporous adsorption resin, desorption with ethanol, recovery of ethanol, and refinement with alumina column so as to give a Siraitia grosvenori extract containing mogroside. Although the method can make up for a part of deficiencies of ethanol elution, the process steps of refinement with ion exchange resin and refinement with alumina column are increased, which may increase the total production cost and be not conducive to large-scale production.
In subcritical water extraction, water is used as the extraction solvent, and it still remains in liquid state when heated to 100 to 374° C. under an appropriate pressure, but the physical and chemical properties thereof are greatly different from those of water at normal temperature and pressure. When the temperature is low, water molecules are close to each other, while under subcritical state, with the elevation of the temperature, the kinetic energy of molecules increases, the intermolecular distance becomes larger, and the fluid microstructure including hydrogen bonding, ion hydration and ion association, cluster structure and the like all change. Therefore, by controlling the temperature and pressure of the subcritical water, the polarity of water is changed within a large range, so that target components with different polarity can be continuously separated and extracted from the mixture. There is no report on the application of subcritical water technology for the desorption from macroporous resins.